| ( | 40 | − | X | ) | ( | 50 | + | 10 | X | X | ÷ | 5 | ) | = | 2100 |
| Left side of the equation = | 40 | ( | 50 | + | 10 | X | X | ÷ | 5 | ) | − | X | ( | 50 | + | 10 | X | X | ÷ | 5 | ) |
| = | 40 | × | 50 | + | 40 | × | 10 | X | X | ÷ | 5 | − | X | ( | 50 | + | 10 | X | X | ÷ | 5 | ) |
| = | 2000 | + | 80 | X | X | − | X | ( | 50 | + | 10 | X | X | ÷ | 5 | ) |
| = | 2000 | + | 80 | X | X | − | X | × | 50 | − | X | × | 10 | X | X | ÷ | 5 |
| = | 2000 | + | 80 | X | X | − | X | × | 50 | − | X | × | 2 | X | X |
| 2000 | + | 80 | X | X | − | 50 | X | − | X | × | 2 | X | X | = | 2100 |